Download Pine Marten-Capercaillie Conflict - Exeter Biosciences

Pine Marten-Capercaillie Conflict
Should pine martens in Scotland be culled?
Dr Fiona Mathews, University of Exeter
The pine marten Martes martes is one Britain’s
rarest and most elusive mammals. After
years of persecution and progressive loss of
its woodland habitat, the species came near
to extinction in the early 1900s, clinging on
primarily in the remote Highlands of northwest Scotland. Recognising its perilous state,
strong protection is now given to the pine
marten under both British and European law.
Over recent years, it has begun to make a
slow comeback. The best populations remain
in the traditional Highland strongholds, but
there is evidence of some recolonisation of
other parts of its former range: anecdotal
reports of its spread in Scotland have been
supported by this summer’s pine marten
survey by The Vincent Wildlife Trust and
Scottish Natural Heritage. Small populations
exist in England and Wales, and there has
been a successful reintroduction to Galloway
Forest in south-west Scotland.
The pine marten is a natural predator of the
eggs and chicks of the charismatic capercaillie
Tetrao urogallus. This ground-nesting bird,
the largest member of the grouse family, is,
like the pine marten, of great conservation
concern. Again like the pine marten, it is
legally protected in Britain, and is a UK
Biodiversity Action Plan (BAP) species.
Unlike the pine marten, which seems to be
in the early stages of recovery, capercaillie
populations are in steady decline. Proposals
have therefore been made by the Scottish
Gamekeepers’ Association for licensed culls
of pine martens in selected areas in order to
promote capercaillie conservation. In view
of the pine marten’s peripheral role in the
capercaillie’s decline, The Mammal Society is
extremely concerned about these proposals
and is urging other conservation organisations
to join with us in opposing them.
8
The capercaillie in Britain
The capercaillie is a cold-adapted, groundnesting bird of the boreal forest zone and
mountain ranges of northern and northeastern Eurasia. It is dependent on conifer
forests with an open canopy, a rich internal
structure and a dense
ground cover in which
Vaccinium shrubs are
abundant. Pine martens
and capercaillie have coexisted across northern
Europe for 12,000
years; across its range,
capercaillie populations
breed successfully in the
presence of pine martens
and a range of other
predators. However, the conservation status
of the capercaillie in Britain is particularly poor.
Following its extinction in Britain and Ireland
in about 1770 (probably due to the combined
effects of deforestation and over-hunting),
the capercaillie was reintroduced to Scotland
in 1837, using Swedish stock. It thrived in
central, north and north-east Scotland until
the mid-1970s, but then began a sustained
decline that now threatens the survival of the
capercaillie in Britain for the second time. A
survey in Scotland in 2009 suggested that
the population had fallen to 1,268 birds; this
is 36% lower than the previous estimate in
2003/04. Currently, about three-quarters of
the capercaillie population is found in forests
in Badenoch and Strathspey in north-east
Scotland.
The survival, breeding success and
productivity of capercaillie populations are
influenced by many factors. Of these, the
most important appear to be habitat and
weather. Woodlands that are small and
fragmented, and those with shrub layers
heavily browsed by
deer, may not support
successful breeding
attempts. In addition,
wetter Junes, part of
a long-term weather
trend in Scotland,
adversely affect the
survival of chicks. It
is also thought that
winter disturbance by
skiers and hill walkers
may affect adult
survival. Mortality has also been caused by
collisions with deer fences (many of which
were installed in an attempt to reduce deer
browsing which was degrading capercaillie
habitat). Finally, predation of eggs and
chicks by foxes, corvids and other predators
influences breeding success. Substantial
effort has been invested by land managers
in habitat management and predator control
(especially of foxes and crows) to conserve the
capercaillie population in north-east Scotland.
This survey found no
evidence to suggest
that pine martens
are impacting upon
capercaillie breeding
success
Pine marten conservation
The pine marten is a native carnivore that
mainly occupies wooded habitats, where it
takes a wide range of food including small
rodents, birds, invertebrates and fruit. The
animals are long-lived and solitary; they breed
slowly (two or three kits is a typical litter size in
Scotland), and live at low population densities.
These characteristics make it difficult for pine
marten populations to sustain any additional
mortality, and they struggle to recover from
local extinctions. The pine marten has a
highly restricted distribution in Britain following
a historical contraction in its range due to
deforestation and predator control. In the
mid 1990s, the population in Scotland was
estimated to be just 3,500 animals. While the
estimate needs to be revised in the light of
new information on patterns of distribution
and abundance, it remains rare, and the
species has certainly not yet recolonised
more than 15% of its historical British range.
The pine marten’s ability to climb and its
tendency to predate game birds means that
it is not popular on some sporting estates in
Scotland; it has been suggested that predator
control may have restricted the pine marten’s
recolonisation of some areas such as northeast Scotland.
Mammal News Autumn 2012 • www.mammal.org.uk
Recent studies of pine marten
predation and capercaillie in
Scotland
A series of research projects has sought to
inform decisions about the role of pine marten
predation in capercaillie conservation. A 1995
study in 14 forests found no link between
capercaillie breeding success and a pine
marten abundance/activity index. A study
in Abernethy Forest, where pine martens
are particularly abundant, revealed that 39%
of capercaillie nests were predated (where
other predators were controlled, around a
third of nests were lost to pine martens); this
level of nest loss was close to the mid-range
among other studies in Scotland and in
Europe. A recent study of the impacts of
various predators on capercaillie in north-east
Scotland confirmed that signs of pine martens
were more abundant than in 1995. However,
no evidence was found of a relationship
between pine marten abundance and any of
the three measures of capercaillie breeding
success, leading to the conclusion that:
‘This survey found no evidence to suggest
that martens are impacting upon capercaillie
breeding success’. A multivariate analysis
of long-term capercaillie brood count data
confirmed that breeding success is strongly
influenced by weather. When the effects
of weather and predator variables were
considered together, some measures of
capercaillie breeding success varied negatively
with an index of marten abundance.
Would removing pine martens
help the capercaillie?
Pine marten predation is peripheral among
the factors influencing the success of
capercaillie populations. A high profile
focus upon the predation issue would create
the misleading impression that a complex
ecological problem (the capercaillie’s decline
in Scotland) can be simply resolved by
removing a scarce, protected predator; and
it would inevitably deflect attention away from
more fundamental factors.
Strong evidence is available that martens
have no net negative impact across Scotland
on capercallie populations. Pine marten
predation of capercaillie nests is a natural
process; the two species have co-evolved in
a predator-prey relationship that has persisted
across northern Europe for 12,000 years;
outside Scotland capercaillie populations
thrive in the presence of pine martens and
other predators. Despite a substantial input
of conservation effort, the Scottish capercaillie
population is in the late stages of a steep
decline that began in the 1970s; the pine
marten’s role in this process is peripheral at
most. In this context, proposals to remove the
pine marten to ‘save the capercaillie’ appear
strategically flawed.
any change in current policy should be
considered. The ‘pilot’ scale at which a
cull could be conducted without potentially
compromising the conservation status of
pine martens would not allow statisticallyrobust conclusions to be drawn, and would
therefore not provide the evidence required.
If we imagine the very optimistic scenario
where controlling martens increased the
average number of chicks raised per hen
from the current level of 0.4 to 0.6 (based on
what might be expected if all predation were
avoided and all eggs hatch), then it would take
a study of 198 trial nest sites where predation
is controlled and another 198 control nests
sites just to be confident the change really
was due to marten removal and
not just chance fluctuation.
Culls on such a scale are
unquestionably outside
the range that could be
considered without seriously
compromising pine marten
conservation. Smaller
studies would simply provide
anecdotal evidence and
could not be used to justify
policy decisions. The recent
government U-turn on
buzzard removal to benefit
pheasant stocks, and the
rumbling controversy
over how to interpret
the badger removal trial,
must surely indicate that
such serious changes
in policy should only
be contemplated on
the basis of the highest
quality of evidence.
capercaillie’s decline, The Mammal Society
accepts that, in the final stages of that
decline, normal levels of predation by pine
martens could become an additional pressure.
However, given the peripheral nature of its
role, and recognising that the pine marten is
a scarce, protected mammal still recolonising
its former range, The Mammal Society does
not accept that the removal of pine martens
is justified by the questionable benefits to
capercaillie conservation. Furthermore, a
focus on pine marten removal would inevitably
deflect attention away from the fundamental
causes of the capercaillie’s decline.
Summary
The capercaillie population
in Scotland, which is derived
from non-native stock, is
in long-term decline. This
decline is due mainly to altered
weather patterns and the lack
of suitable habitat. Although
there is no evidence to suggest
that predation by pine martens
is an influential factor in the
The Mammal Society’s Position
•
The evidence to suggest that pine marten predation is an important factor influencing
capercaillie breeding success is very poor.
•
The success of capercaillie populations is influenced by a complex suite of interacting
factors, both natural and human, that affect breeding success. Predation is just one of
these factors.
•
A proposal to remove one protected native species (the pine marten) to protect another
(the capercaillie) is highly questionable.
What other issues have
to be considered?
•
Removing, even temporarily, the protection for a species which is likely to be highly
persecuted because of its tendency to predate game birds, sets a precedent for future
culling and for culling outside the selected areas.
If one accepts that the removal of pine
martens may bring some benefits to
capercaillie conservation, there are additional
issues that must be considered before
•
Even setting aside ethical concerns, the proposed ‘trials’ would lack the sample size to
produce statistically rigorous results. It would therefore not be possible to conclude from
them whether culling could contribute usefully to capercallie conservation or not.
Mammal News Autumn 2012 • www.mammal.org.uk
9